Not applicable.
Not applicable.
The invention relates to medical devices, and more particularly to prosthetic joint components.
Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. A typical knee prosthesis includes a tibial component, a femoral component, a femoral stem assembly, and a patellar component. The femoral component generally includes a pair of spaced apart condylar portions, the superior surfaces of which articulate with a portion of the tibial component. The femoral stem assembly provides lateral stability, and it typically includes a member that is inserted within a reamed intramedullary canal at the distal end of a femur. The stem is typically coupled to the femoral component by a collar and bolt.
Although modular systems can provide an advantageous reduction in joint component inventory, known systems do not fully address the problems associated with variations in intramedullary canal geometry. Specifically, the variations in the morphology of the intermedullary canal often do not match the geometry of the stem, forcing the surgical positioning of the femoral component that is mated to the stem to be determined by considerations other than the shape of the canal.
For example, if the implant geometry does not match the canal geometry, the stem of the implant can contact the cortical wall of the intramedullary canal while the stem is being impacted. This problem can be further complicated when a femoral stem is mated to a sleeve that increases the effective length of the stem so that it is in a bowed portion of the intramedullary canal.
In response to the above problems, a surgeon may be forced to remove the stem (or entire component) and replace it with a stem having a smaller diameter or shorter length, even if the replacement stem is thought to be less suitable than the original stem, but for the improper fit. Also, the surgeon may have to cut notches in the femur to accommodate a shifted femoral component.
Therefore, despite the existence of joint prostheses having modular components, there remains a need for a modular joint prosthesis that has greater versatility to accommodate differing patient anatomy and joint conditions.
The present invention relates to a modular knee joint prosthesis having improved versatility. Components of the modular prosthesis of the invention are able to be used with both right and left side prostheses.
The present invention provides a modular knee prosthesis which includes a femoral component having a pair of spaced apart condylar portions and a boss structure extending between the condylar portions. The boss structure has a top superior surface that extends generally horizontally in a transverse plane and an opposed inferior surface which has a cavity formed therein that terminates in a substantially spherically shaped endwall. The boss structure further includes an aperture which extends between the mounting and securing surfaces of the boss structure. The knee prosthesis further includes a stem component which has a proximal end and a distal end that is mountable through the boss aperture.
A mounting surface is provided which may be either integrated into the stem component or provided as a separate collar component for varying the angulation of the stem component relative to the femoral component. The mounting surface is oriented substantially transverse to a longitudinal axis of the stem member such that the mounting surface and the top surface of the boss structure define a selected mounting angle therebetween. Finally, the knee prosthesis includes an attachment nut having a spherically shaped superior surface for engaging the spherically shaped endwall of the boss structure to secure the stem member to the femoral component.